Of course it's the season for gatherings of friends and neighbors. But increasingly, 'tis also the season for solar power — and I'm speaking of "season" in the eon sense. Friday night, I joined about 30 other guests at a neighbor's home not to share holiday cheer but to learn details about home photovoltaic installations.

Our host was Laurel Kayne, an advocate and enthusiast whose family installed two solar thermal panels. Tyler Austin, an energy consultant with Borrego Solar, was there as well, and after an extended social hour, he gave a presentation on solar considerations.

Other guests included those who live on Kayne's street, but the largest portion of the group were her Arlington teammates — she is a co-captain — in the Energy Smackdown, which pits them against teams from Medford and Cambridge. Once the solar discussion had begun, several folks were taking notes.

Ordinarily, I would mock the use of "energy consultant" on a business card, as one of those odious little lies that salesmen tell to avoid saying they're salesmen. But faced with a large group of motivated, self-selected potential customers, Austin's opening statement was, "Solar is the last thing you should do. Conservation pays back the fastest."

This is the basic truth of sustainability, but still, he earned instant credibility with me for saying it. For starting with it.

Later in the evening, this sense was bolstered when Kayne told of how she badgered Austin with requests to install photovoltaics, in addition to solar thermal, but he was insistent that her roof exposure wasn't suitable. (To reap sufficient energy, panels must face fairly close to true south, and at the proper angle, which is 30 degrees around here.)

People were impressed at his refusal to sell, which he took a moment of kudos for before making clear that the substantial rebates that are available for solar installations are dependent of demonstrating solar potential. (Why help pay for panels that face, say, north, or are shaded all afternoon?)

The issue and timing of payback arose more than once, and Austin had a very good salesman's answer: "What's the payback on your electrical bill? Never. At least your money is going into an asset on your house instead of to the utilities." Great point!
Some other tidbits from the evening:

* pvwatt.com has a solar calculator.

* The average installed cost in Mass. is $8.15 per watt.

* A rule of thumb says that for every dollar you save in electricity, you add $20 in equity to your house.

* People tend to conserve more, once they have installed solar. One implication from this is that it may be better to purchase a little less than you need, rather than a little more.

* Until five or six years ago, electricity rates rose by about 5 percent a year. Since then, they've been going up about 13 percent a year, Austin said.